I've always heard (from docs) that 37 weeks is full-term. However women I know who were at risk of preterm labor or who threatened premature labor were allowed to go into labor after 34 weeks, if it started on its own. I know a couple whose doctors just "wanted to get them to 34 weeks" before feeling ok about the baby coming. I guess this is just considered enough time developmentally? And in those cases, the women were given steroids to mature babies lungs by 34 weeks.

Babies brains aren't even fully developed at 37 weeks. There's been a lot of new research showing drastic brain growth between 37 and 39 weeks. I wouldn't feel comfortable with a doctor being OK with babies coming at 34 weeks.